<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>文档流</title>
  <style>
    body {
      margin: 0;
    }

    .one {
      height: 50px;
      background-color: lightcyan;
    }

    .two {
      height: 50px;
      float: left;
      background-color: lightgoldenrodyellow;
    }

    .three {
      height: 50px;
      background-color: lightgreen;
    }
  </style>

</head>

<body>

  <div class="one"></div>
  <div class="two"></div>
  <div class="three"></div>
</body>

</html>